Sunday, April 1, 2012

Quadcopter: Frame Assembly

I spent some time this last week making the center frame plates and assembling the main frame components. I took some pictures while doing it so you can see the process.

Before making the center plates, I built up a single arm assembly. A speed control is temporarily attached so I can test the motor. For how small the motor is, it produces an amazing amount of thrust. We will see if it has the torque to keep up with the speed changes coming from the ESC and be able to keep the craft stable, but I am optimistic.

Here is the bottom side of the the motor attachment point. The motor is held on by 4x #2-56 steel socket head cap screws. On this side you can see the nuts which the screws thread into to hold everything together. Once I am sure everything will work, I will be applying glue to prevent these from coming loose in flight.

The center plates are made from two 6" (400mm) square pieces of plywood. This is 1/8" (3mm) thick 6 layer light ply I purchased from Tower Hobbies. Above you can see my markings showing where to drill the holes for the #4-40 screws that will hold these center plates against the carbon fiber motor mount arms. I drilled holes in the four corners first, and held the two plates together by these four holes. After that I drilled the remaining functional holes. This allowed me to make two nearly identical plates very quickly. Once all of the holes were drilled, I moved the bolts away from the corners (see upper right corner in the above picture). I then cut off the corners off.

Here you can see I have gathered all of the main frame components together to begin assembly.

All of the arms are assembled. One of the arms has been attached to the main plates. I used 4x #4-40 nylon pan head screws to attach the arms. I went with nylon as is it is much lighter than steel and I don't need the strength of steel since the arms will be glued as well once I attach everything else. The screws are threaded into nylon nuts on the far side.

All of the arms have been attached. The frame feels light and very stiff. The center to center measurement from one motor to the opposite motor is slightly more than 16" (400mm). With 8" props, the overall width will be 24" (600mm).

Here's a side view where you can see how the plates sandwich the motor mount arms. I am considering making thin spacers to spread the two plates apart so that I can hide the motor ESC between these main plates.

With the frame assembled, I placed it on a scale and stacked all of the other parts on top of it to see what the final flying weight will be. Including the battery, the scale read slightly over 1lbs (500g). This is the target weight I had in mind when I started designing this thing, so I am happy to be on target.

That is all for now. Let me know if you have any questions.

Thanks for reading and please sign up on the right if you want to be automatically notified when I post more updates.